1. Field of the Invention
The present invention relates to a sensor signal processing system for processing an output signal of an angular velocity sensor (angular accelerometer) or the like for producing a detection signal that corresponds to a physical phenomenon and relates to a detector that is used for the system.
2. Description of the Prior Art
Conventionally, an angular velocity sensor (an angular accelerometer, also called a gyro sensor) for detecting an angular velocity of an object has been used for detection of shake or movement of a video camera, a navigation device, detection of a roll angle for determining a release timing of side air bags, or an attitude control of a vehicle or a robot.
Such an angular velocity sensor includes a beam type and a tuning fork type. Among those types, a tuning fork gyro sensor is widely used because it can be vibrated easily and has a high Q value (see patent documents 1-3 below).
The tuning fork gyro sensor has a structure including a substrate of a tuning fork (an oscillator) having a plurality of arm portions and a base portion (node portion) made of a piezoelectric material such as a lithium niobate (LN) and a plurality of electrodes for drive and detection that are disposed on front, rear and side faces.
This angular velocity sensor has sensitivity that varies in accordance with temperature. For example, an LN gyro sensor made of a piezoelectric material such as a lithium niobate (LN) has sensitivity-temperature characteristics as shown in FIG. 8, in which the sensitivity decreases as the temperature rises. The sensitivity-temperature characteristics in the example shown in FIG. 8 have a rate of approximately −1100 ppm/° C.
In order to compensate such sensitivity-temperature characteristics of the angular velocity sensor, various countermeasures have been adopted. For example, the patent document 1 below discloses a method of a conventional technique, in which, with respect to an angular velocity sensor, discrete correction data of sensitivity to temperature is memorized, and the correction data that correspond to a temperature detected by a temperature sensor in the vicinity of the angular velocity sensor are read out for performing the correction. However, this method has some disadvantages in that it is difficult to perform consecutive corrections and that it is troublesome to obtain the correction data in advance and that a system configuration becomes complicated.
In addition, the patent document 3 proposes a method for a semiconductor integrated circuit that constitutes a detection circuit (a detector). In this method, an internal resistor having some temperature characteristics and an external resistor having little temperature characteristics are used respectively as an input resistor and an output resistor of a differential amplifier circuit, so that an amplification factor of the amplifier circuit has temperature characteristics. Thus, the sensitivity-temperature characteristics of the angular velocity sensor can be cancelled.
[Patent Document 1] Japanese unexamined patent publication No. 2002-372422
[Patent Document 2] Japanese unexamined patent publication No. 2003-247828
[Patent Document 3] Japanese unexamined patent publication No. 11-148829
However, the conventional method proposed in the above-mentioned patent document 3 has a disadvantage in that temperature-gain characteristics of an amplifier circuit in a semiconductor integrated circuit are determined uniquely by temperature characteristics of an internal resistance.
On the other hand, sensitivity-temperature characteristics of an angular velocity sensor may alter in accordance with a variation or a lot number of a manufacturing process or are changed along with a design change of the angular velocity sensor.
Therefore, in order to enable the similar compensation for each of the angular velocity sensors, it is necessary to revise the semiconductor integrated circuit so as to change specifications of the detection circuit responding to the change of the sensitivity-temperature characteristics. However, designing and manufacturing a semiconductor integrated circuit takes a long time and needs high cost, so this method is not good in flexibility.
In addition, if the sensitivity-temperature characteristics have a large ratio, it is necessary to use a large correction coefficient of the temperature characteristics corresponding thereto. Therefore, it is necessary to use a multistage amplifier circuit, which causes a large scale of circuit and a higher cost of manufacturing the semiconductor integrated circuit.